57 research outputs found
Good practice guide on the electrical characterisation of graphene using contact methods
The electrical characterisation of graphene, either in plane sheets or in properly geometrised form can be approached using methods already employed for thin film materials. The extraordinary thinness (and, correspondingly, the volume) of graphene, however, makes the proper application of these methods difficult. The electrical properties of interest (sheet electrical resistivity/conductivity, concentration and mobility of charge carriers) must be indirectly derived from the measurement outcome by geometrical and electrical modelling; the assumptions behind such models (e.g., uniformity and isotropy, effective value of the applied fields, etc.) require careful consideration. The traceability of the measurement to the International System of units and a proper expression of measurement uncertainty is an issue. This guide focuses on contact methods, that is method where the graphene sample surface is physically contacted with metallic electrodes. A companion guide about non-contact and high-throughput methods is also available. The methods discussed are: the in-line four-point probe (4PP); the van der Pauw method (vdP) for sheet resistance measurement; the van der Pauw method for charge carrier mobility measurement; the electrical resistance tomography (ERT); the coplanar waveguide method (CPW). For each method, a corresponding measurement protocol is discussed, which describes: the measurement principle; sample requirements and preparation; a description of the measurement equipment / apparatus; calibration standards and ways to achieve a traceable measurement; environmental conditions to be considered; a detailed measurement procedure, with specific hints to achieve a reliable measurement; modeling and data analysis to determine the electrical property of interest; considerations about the expression of measurement uncertainty
Resolvin D1 Halts Remote Neuroinflammation and Improves Functional Recovery after Focal Brain Damage Via ALX/FPR2 Receptor-Regulated MicroRNAs
Remote damage is a secondary phenomenon that usually occurs after a primary brain damage in regions that are distant, yet functionally connected, and that is critical for determining the outcomes of several CNS pathologies, including traumatic brain and spinal cord injuries. The understanding of remote damage-associated mechanisms has been mostly achieved in several models of focal brain injury such as the hemicerebellectomy (HCb) experimental paradigm, which helped to identify the involvement of many key players, such as inflammation, oxidative stress, apoptosis and autophagy. Currently, few interventions have been shown to successfully limit the progression of secondary damage events and there is still an unmet need for new therapeutic options. Given the emergence of the novel concept of resolution of inflammation, mediated by the newly identified ω3-derived specialized pro-resolving lipid mediators, such as resolvins, we reported a reduced ability of HCb-injured animals to produce resolvin D1 (RvD1) and an increased expression of its target receptor ALX/FPR2 in remote brain regions. The in vivo administration of RvD1 promoted functional recovery and neuroprotection by reducing the activation of Iba-1+ microglia and GFAP+ astrocytes as well as by impairing inflammatory-induced neuronal cell death in remote regions. These effects were counteracted by intracerebroventricular neutralization of ALX/FPR2, whose activation by RvD1 also down-regulated miR-146b and miR-219a-1-dependent inflammatory markers. In conclusion, we propose that innovative therapies based on RvD1-ALX/ FPR2 axis could be exploited to curtail remote damage and enable neuroprotective effects after acute focal brain damage
Curvature-enhanced localised emission from dark states in wrinkled monolayer WSe2 at room temperature
Localised emission from defect states in monolayer transition metal
dichalcogenides is of great interest for optoelectronic and quantum device
applications. Recent progress towards high temperature localised emission
relies on the application of strain to induce highly confined excitonic states.
Here we propose an alternative paradigm based on curvature, rather than
in-plane stretching, achieved through free-standing wrinkles of monolayer
tungsten diselenide (WSe2). We probe these nanostructures using tip-enhanced
optical spectroscopy to reveal the spatial localisation of out-of-plane
polarised emission from the WSe2 wrinkles. Based on the photoluminescence and
Raman scattering signatures resolved with nanoscale spatial resolution, we
propose the existence of a manifold of spin-forbidden excitonic states that are
activated by the local curvature of the WSe2. We are able to access these dark
states through the out-of-plane polarised surface plasmon polariton resulting
in enhanced strongly localised emission at room temperature, which is of
potential interest for quantum technologies and photonic devices
Loss of miR-107, miR-181c and miR-29a-3p promote activation of Notch2 signaling in pediatric high-grade gliomas (pHGGs)
The mechanisms by which microRNAs control pediatric high-grade gliomas (pHGGs) have
yet to be fully elucidated. Our studies of patient-derived pHGG tissues and of the pHGG cell line
KNS42 revealed down-regulation in these tumors of three microRNAs, specifically miR-107, miR-181c,
and miR-29a-3p. This down-regulation increases the proliferation of KNS42 cells by de-repressing
expression of the Notch2 receptor (Notch2), a validated target of miR-107 and miR-181c and a
putative target of miR-29a-3p. Inhibition (either pharmacologic or genetic) of Notch2 or re-expression
of the implicated microRNAs (all three combined but also individually) significantly reduced KNS42
cell proliferation. These findings suggest that Notch2 pathway activation plays a critical role in
pHGGs growth and reveal a direct epigenetic mechanism that controls Notch2 expression, which
could potentially be targeted by novel forms of therapy for these childhood tumors characterized by
high-morbidity and high-mortality
Resonant band hybridization in alloyed transition metal dichalcogenide heterobilayers
Bandstructure engineering using alloying is widely utilised for achieving
optimised performance in modern semiconductor devices. While alloying has been
studied in monolayer transition metal dichalcogenides, its application in van
der Waals heterostructures built from atomically thin layers is largely
unexplored. Here, we fabricate heterobilayers made from monolayers of WSe
(or MoSe) and MoWSe alloy and observe nontrivial tuning of
the resultant bandstructure as a function of concentration . We monitor this
evolution by measuring the energy of photoluminescence (PL) of the interlayer
exciton (IX) composed of an electron and hole residing in different monolayers.
In MoWSe/WSe, we observe a strong IX energy shift of
100 meV for varied from 1 to 0.6. However, for this shift
saturates and the IX PL energy asymptotically approaches that of the indirect
bandgap in bilayer WSe. We theoretically interpret this observation as the
strong variation of the conduction band K valley for , with IX PL
arising from the K-K transition, while for , the bandstructure
hybridization becomes prevalent leading to the dominating momentum-indirect K-Q
transition. This bandstructure hybridization is accompanied with strong
modification of IX PL dynamics and nonlinear exciton properties. Our work
provides foundation for bandstructure engineering in van der Waals
heterostructures highlighting the importance of hybridization effects and
opening a way to devices with accurately tailored electronic properties.Comment: Supporting Information can be found downloading and extracting the
gzipped tar source file listed under "Other formats
Phase transitions in contagion processes mediated by recurrent mobility patterns
Human mobility and activity patterns mediate contagion on many levels,
including the spatial spread of infectious diseases, diffusion of rumors, and
emergence of consensus. These patterns however are often dominated by specific
locations and recurrent flows and poorly modeled by the random diffusive
dynamics generally used to study them. Here we develop a theoretical framework
to analyze contagion within a network of locations where individuals recall
their geographic origins. We find a phase transition between a regime in which
the contagion affects a large fraction of the system and one in which only a
small fraction is affected. This transition cannot be uncovered by continuous
deterministic models due to the stochastic features of the contagion process
and defines an invasion threshold that depends on mobility parameters,
providing guidance for controlling contagion spread by constraining mobility
processes. We recover the threshold behavior by analyzing diffusion processes
mediated by real human commuting data.Comment: 20 pages of Main Text including 4 figures, 7 pages of Supplementary
Information; Nature Physics (2011
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